Rheostat



C. WILLMS.

(No Model.)

RHBOSTAT.

Patented May 24, 1892.

UNITED STATES PATENT i OFFIcE.

CHARLES \VILLMS, OF BALTIMORE, MARYLAND.

RH EOSTAT.

SPECIFICATION forming part of Letters Patent No. 47 5,528, dated May 24, 1892.

Application filed January 14, 1892. Serial No. 418,036. (No model.)

To all whom it may concern.-

Beit known that I, CHARLES WILLMs, a citizen of the United States, residing at Baltimore, in the State of Maryland, have invented certain newand useful Improvements in Rheostats, fully described and represented in the following specification and the accompanying drawings, forming a part of the same.

The object of the present invention is to improve the construction of rheostats or ourrent-regulators, and especially to provide an improved resistance material therefor. I have devised, also, an improved rheostat employing my improved resistance material and a method of making the same, which forms part of the present invention.

It is desirable that the resistance material used in rheostatsshould be of considerable resistance and at the same time have sufficient conductivity for the purposes for which the rheostat is designed. Such resistance materials are commonly formed of conductng material in a state of fine division, and while various materials are used for this purpose finely-divided carbon, in the form of lamp-black or graphite, has been found satisfactory and is now in general use, being usually mixed with glue or other material to form a mass of the required density.

I provide an improved resistance material in which the desired relations between resist ance and conductivity arebetter attained than in resistance materials previously in use by mixing with a resistance material containing fin ely-divided carbon or other suitable finelydivided conducting material particles someivhat larger than those of the conducting material and of high conductivity. I may use as the larger particles filings of copper, brass, or similar metal of high conductivity; but it will be understood that similar particles of other material may be usedsuch as granular carbon-and hat the particles may be produced by any other method than filing, the particles being described as filings only to indicate approximately their preferred slze.

My improved resistance material is of general application in rheostats, and it may be formed and applied in any suitable manner;

but the invention has'been made in connection with that class of rheostats used for light currents in which the body of resistance ma.- terial consists of a thin layer of plastic material, and I have devised a special method of forming this by which this body of resistance material is rendered more durable, the tendency to crack and peel oif is lessened, and by which the resistance material may be more readily applied tOfOllIl a uniform body of the slight thicknessrequired.

The method I employ in forming my rheostat is as follows: I first paint upon the body of the rheostat a base of the same shape as the body of resistance material desired, this base consisting of a mixture of adhesive material and finely-divided carbon, preferably in the form of graphite, and upon this baseI sift, preferably by shaking it from an ordinary pepper-box, the required amount of metal filings or other similar particles of high conductivity. I then subject the rheostat to pressure and thus force the metal filings into and through the body of the base, so as to form a resistance material uniform throughout. The form of the adhesive base and the steps necessary in completing the rheostat depend upon the particular form of rheostat with which my resistance material and method I are employed.

In forming the adhesive base I may use glue or any other suitable adhesive material, and

with adhesive materials of a certain consistency the method may be varied by applying the adhesive material alone to form the base and completing the resistance material by sifting over and pressing into it a mixture of the finely-divided carbon and the larger particles. I have found, however, that the best results are attained with sugar-water, with which the fine carbon, preferably in the form of powdered graphite, is mixed to forma mixture of the consistency of paint. This is applied with a brush to the face of the plate, the number of coats being varied withthe thickness of resistance material desired. The larger particles are then added and the body of resistance material completed, as already described. The sugar-water possesses many advantages over glue, the most important of which is that the body of resistance material ICO formed thereby is much tougher and harder and resists better the action of heat, which feature is very important with heavy currents.

For a full understanding of my invention a detailed description of a rheostat embodying the same will now be given, and the features forming my invention specifically pointed out in the claims.

In theaccompanying drawings, forming a part of this specification, Figure 1 is a plan view of the rheostat. Fig. 2 is a reverse plan of the same. Fig. 3 is a section on the line 3 of Fig. 1, and Fig. 4 is a section on the line 4 of Fig. 2.

Referring to said drawings, A is a block of insulating material, preferably-of rubber, and a b the binding-posts mounted thereon and forming the terminals. The binding-posts a I) pass through the block A and connect, respectively, with. metallic contact-plates c d, secured to the underside of the block. The plate 0 forms the contact-plate from which the current passes through the insulating material, and the plate d connects by means of a stud e, extending through the block, with a contact-arm f, moving in' the arc of a circle over the top of the block and actuated by means of an insulating thumb-piece 9, connected to the stud e and arm f by a cross-pin, as shown,or in any other suitable manner. lhe contact-arm f at its outer end moves over and makes contact with a series of conductors, consisting in the form shown of pins h, preferably level with the top of the block A and extending through the same. \Vhile the conductors are shown as pins and as of the same size on both sides of the block, it will be understood that they may be of any other suitable construction and that the area of their surface on the under side of the block may be increased in any suitable manner if a wider conducting-surface in contact with the resistance material be desired. The conductors h extend about the block in the arc of a circle, which is shown in the drawings as nearly. complete; but it will be understood that the length of the are may be varied, as desired, and may be any portion of a circle, and that the circular form is not essential, but is adopted simply on account of convenience in making contact with a single point through an arm swinging in the arc of a circle.

The resistance material 2 is shown as applied in a path of decreasing width from the contact-plate 0 through the circuit of the conductors h, as usual in this class of rheostats, so that by the movement of the arm f over the pins a greater or less length of the resistance material may be thrown into the circuit, the resistance increasing as the width of the path of resistance material diminishes, and

the current being conveyed through the resistance material and that one of the conductors h with which the arm f is brought into contact to binding-post a to complete the circuit. \Vith the small current used with rheostats of this construction a comparatively thin body of resistance material is required, and much difficulty has been found 1n producing a unifornrlayer of resistance material, and such rheostats have not been durable on account of the tendency of the resistance material to crack and peel off.

In carrying out the method forminga part of the present invention in the preferred manner I first paint upon the under SUlB Of the block A a mixture of adhesive material and finely-divided conducting material,preferably carbon, in the form of powdered graphite, to form a picture of the body of resistance material to be applied and to cover theconductore and contact-plate c, this mixture forming a base closely adherent to the block and plate, so that the resistance material is firmly sccured thereby. Upon this base I shake from an ordinary pepper-box or similar bog: the required amount of metal filings or'simllar particles of some material of high conductivity, so as to entirely cover the base. I then submit. the rheostat to pressure, by which the carbon and metal filings are forced into and intimately mixed with the base to form the resistance material and the loose particles are then dusted out. As above stated, the adhesive material used in forming the base by tlns method is preferably sugar-water or some equivalent thereof, although other adhesive materials may be used with fairly good re sults. r

In the modified method above described, in which the base is formed of adhesive material alone, I apply the adhesive material to the face of the block without covering the pins h and plate 0, and then sift over it a mixture of finely-divided conducting materialsuch as powdered graphite and the metal filings or similar particlesand then press these materials into the glue and dust off the loose particles, as before. If care has been taken in applying thebasc, it is now necessary for the completion of the rheostat only to cover the conductors h and the plate 0 with a compound of graphite and adhesive material, and then dust over this material the metal filings, this also being preferably submitted to pressure so as to consolidate the filings and resistance material. Itwill probably be more convenient, however, to apply the base without regard to the conductors h and plate 0, so that a resistance material extending over the whole surface of the block between the pins and about the plate shall be secured. Then this is done, however, it is evident that the adhesive material forms a layer between the resistance material proper and the conductors and plate which would interfere with the conduction of the current. I therefore in carrying out my method scrape off the material from the conductors and plate after the body of resistance material has been applied to the block, as above described, and then apply to the conductors and plate the com pound of graphite and adhesive material, sifting the metal filings over this and pressing in the same, as above explained.

\Vhile I have illustrated my invention as applied to a special form of rheostat employing a thin layer of resistance material, it will be understood that my improved resistance material is of general application in rheostats,

independently of the thickness of the body 3. The method of forming the body of re-.

sistauce material in rheostats, whichponsists in forming an adhesive base of the form of the body of resistance material desired, sifting thereon particles of conducting material, and combining the conducting material with the adhesive base by pressure, substantially as described.

3. The method of forming the body of resistance material in rheostats, which consists in applying a mixture of adhesive material form a base of the form ot-the body of resistance material desired, sifting ther 11 metal filings orsimilar pa rticlesot high conductivity, and combining these particles with the adhesive base by pressure, substantially as described.

t. The method of forming the body of resistance material in rheostats, which consists in applying a mixture of sugar-water or equivalent material and finely-divided conducting material to form a base of the form of the body ofresistance material desired, sifting thereon larger particles of conducting material, and combining the conducting material with the adhesive base by pressure, substantially as described.

5. A rheostat having a supporting block of non-conducting material and a body of reand finely-divided conducting mzierial t0 .sistance material secured to the face thereof by adhesive material and containing finelydivided conducting material and larger particles of metal or other material of high conductivity, substantially as described.

' .In testimony whereof I have hereunto set my hand in the presence of two subscribing witnesses.

. CH. WILLMS.

\Vitnesses:

JAMES J. WARRINGTON, .VM. H. JONES. 

